We propose a simple and elegant technique to directly measure the electric charge on the surfaces of small pixels of III-V and II-VI infrared detectors. Such charges arise from minority-carrier inversion or majority-carrier accumulation layers caused by surface states and exist as 2-dimensional electron or hole gases on the mesa sidewalls. They cause surface current leakage down the sidewalls that dominate the dark current in small pixels. Quantifying the effect of different passivation techniques on surface electric charge is crucial to minimizing sidewall leakage current. In Phase I, we will develop and demonstrate the viability of our measurement technique. In Phase II, we will develop an instrument and study a variety of passivation techniques with the goal of eliminating sidewall leakage in small pixels of Type-II InAs/GaSb strained layer superlattice photodiodes.